The object is our study is to provide a coherent basis for the understanding of the electromagnetic properties and biochemical reactivity of cytochrome P450. Oxidative metabolism by P450 renders a variety of drugs water soluble but also transforms certain chemicals to active carcinogens. The reactive cycle of P450s' has been well characterized and involves four stable states of the enzyme and a fifth, reactive state which carries out the oxidation. Each of the stable states has a number of characteristic electromagnetic properties which can be directly related to the immediate environment around the heme unit as the protein proceeds through the reaction cycle. Using the method of quantum chemistry, we propose to characterize the conformation, electronic structure and spin distribution of each of the stable states of the heme unit. The results will be used to calculate electromagnetic properties which can then be compared to experiment. In this way a realistic model for each of the 4 stages will be obtained which is consistent with experimental behavior and which furnishes a more detailed description of the active site than can be obtained from the experiments alone. The nature of the active species and in particular the oxygen which is transferred from the heme unit to the substrate is not known. Using the same theoretical methods candidates will be characterized and examined for reactivity consistent with the hypothesized mechanism of P450 oxidation.